#include <stdio.h>

int main()
{
int i, j;
char str[81]="123 456 6789";

i = j = 0;
while (str[i] != '\0') {
    if
(str[i]!=' ')
{
        str[j] = str[i];
        
++j;

    }
    i++;
}
str[j]=0;

printf(str);
}